1. Field of the Invention
This invention relates to a remote control signal processing circuit capable of checking remote control signals.
2. Description of the Prior Art
A home appliance (air conditioner or television set, for example) incorporates a microcomputer which receives the remote control signal sent from a remote controller and control the room temperature adjustment or volume adjustment based on the received remote control signal. The remote control signal sent from a remote controller consists of a leader code, custom code, data code and other codes and is usually input to the microcomputer via a preamplifier integrated circuit (IC) for remote control signal receiving. The microcomputer to which the remote control signal is input judges whether the custom code or data code is logic "0" or "1" and detects a leader code, and checks whether the pulse width is normal or not for every code, all through software processing.
A conventional remote control signal processing circuit generally comprises a noise elimination circuit to eliminate noise of the remote control signal, an edge detection circuit to detect the edge of the remote control signal and a timer. The remote control signal is subjected to noise elimination by the noise elimination circuit and then to pulse edge detection by the edge detection circuit. For leader code detection, the edge detection circuit detects a pulse leading edge and interrupts the central processing unit (CPU). The CPU sets a predetermined value at the timer through software processing. While the timer keeps time for the set value, the CPU reads the output level from the noise elimination circuit. If four or more consecutive outputs are at a low level, the pulse is recognized as the leader code, but if not, it is treated as an abnormal (error) pulse. When the pulse is recognized as a leader code, a new value is set at the timer and if the edge detection circuit detects a leading edge while the timer keeps time for the new set value, leader code detection is terminated. If not, the pulse is treated as an error pulse. In addition, the CPU always checks the level of the noise elimination circuit through software processing to judge whether the pulse width is normal or not. In this case, value setting for timer and operation control are performed by the CPU through software processing.
After the leader code detection, the custom code and data code are checked whether they are logic "0" or "1". In this "0" or "1" judgment for the custom code and the data code, each time the edge detection circuit detects a pulse edge, it interrupts the CPU and thereby activates the software for the "0" or "1" judgment and reads the value at the timer. By comparing and operating the timer value at the previous edge detection and the value at the present edge detection, a pulse cycle width for the remote control signal is determined, based on which of "0" or "1" is judged. In this method, it is required to interrupt the CPU and activate the software for operation each time a pulse edge of the remote control signal is detected.
As mentioned above, a conventional remote control signal processing circuit uses software processing for leader code detection, pulse check and "0" or "1" judgment for custom code and data code, which results in a long software processing time and increased program volume. This makes it extremely difficult for a single microcomputer to receive remote control signal and to control the system at the same time.